The Docklands Light Railway (DLR) is an automated light metro system opened in 1987 to serve the redeveloped Docklands area of London. It reaches north to Stratford, south to Lewisham, west to Tower Gateway and Bank in the City of London financial district, and east to Beckton, London City Airport and Woolwich Arsenal.

The system uses minimal staffing on trains and at major interchange stations; the four below-ground stations are staffed to comply with underground station fire and safety requirements. Similar proposals have been made for the Tube.

The DLR is operated under a franchise awarded by Transport for London to KeolisAmey Docklands, a joint venture between transport operator Keolis and infrastructure specialists Amey plc. It was previously run for over 17 years by Serco Docklands, part of the Serco Group. The system is owned by Docklands Light Railway Ltd, part of the London Rail division of Transport for London. In Fiscal Year 2014, the DLR carried 110.2 million passengers. It has been extended several times and further extensions are under consideration.

Light railway is a railway built at lower costs and to lower standards than typical "heavy rail"; it uses lighter-weight track, and is more steeply graded and tightly curved to avoid civil engineering costs. These lighter standards allow lower costs of operation, at the price of slower operating speeds and lower vehicle capacity.

Narrow gauge

In countries where a single standard gauge is dominant, the term light railway does not imply a narrow gauge railway. Most such narrow gauge railways operate as light railways, but not all light railways need be narrow gauge. After Spooner's development of steam-haulage for narrow gauge railways the prevailing view was that the gauge should be tailored according to the traffic, "the nearer the machine is apportioned to the work it has to do the cheaper will that work be done". From the 1890s though it was recognised that cost-savings could be made in construction and operation of a standard gauge railway, "light axle-loads and low speeds, not gauge, are the first condition of cheap construction and economical working. Gauge is quite a secondary factor."Break of gauge now became an important factor and there was much concern over whether this would become an additional cost for the transhipment of goods, or whether this was over-emphasised compared to the amount of warehousing and handling needed anyway. The Irish railway system in particular became a good example of a broad gauge main line system with many independent narrow gauge, 3 ft (914 mm), light railway feeder branch lines.